The long term objective of this research is to enhance the quality of life of the elderly through improved oral health. The focus of the present proposal is to identify age-related changes in masticatory function with the goal of developing strategies for maintaining oral function with aging. Studies will be carried out using well-defined human populations consisting of males, females, Mexican Americans and Non-Hispanic Whites. A feature of the proposal also is to investigate mechanisms of age-related change in masticatory function using an animal model - the Fischer 344 rat. The proposal will test the hypothesis that decline of oral health in old age is due in part to altered function of the joints and muscles of mastication. The hypothesis will be tested by executing specific aims: (i) In adult and aged individuals (35-75+ years old, male, female, Mexican American, Non-Hispanic White) measure masticatory efficiency, bite force, cross-sectional area of masseter muscle, temporomandibular disorders and proprioceptive sensitivity of oral structures. (2) Assess effects of tooth loss and occlusal status on factors listed in (i). (3) In Fischer 344 rats measure age-related variation in mass, structure (fiber diameter and fiber number) and composition (fiber type) of masseter muscles. (4) In Fischer 344 rats measure in vitro the maximum active tension, passive compliance, endurance and enzyme activities related to energy metabolism in masseter muscles. Measurements will be conducted using 320 volunteers per year over a four year period. These non-invasive measurements will establish age- related changes in bite force, temporomandibular function and proprioceptive sensitivity. The extent to which these changes are modulated by gender, ethnicity, tooth loss, occlusal status, loss of muscle mass and disease will be determined. Experiments using a rodent model which is widely used in aging studies (Fischer 344 rats) will determine mechanisms of age-related change in function of rat masseter muscles. In particular, effects of age on muscle strength, endurance, capacity for energy metabolism, elasticity, composition, size and number of muscle fibers will be measured. These experiments will also demonstrate whether effects of aging and gender on masseter muscle function in rodents are consistent with those determined in human volunteers. The proposed research will therefore establish the extent to which aging affects masticatory function in particular segments of the population and will assess the impact on these effects of tooth loss, joint disorders and systemic disease. Since efficient masticatory function represents an essential first step towards successful nutrition, these experiments will provide important information relating oral health to well-being of the elderly.